Coating cathodes



COATING CATHODES Filed June 20, 1941 INVENTOR 61 .5. EVA/VS MSIMh L ATTORNEY Patented Nov. 19, 1946 COATING CATHODES George S. Evans, East Orange, N. J assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation ofPennsylvania Application June 20, 1941, Serial No. 398,915

4 Claims.

My invention relates toelectrodes and especially to the coated type of electrode.

An object of my invention is to provide an evenly coated electrode.

Another object of my invention is to provide the desired thickness of coating in the desired areas.

Another object of my invention is to provide means for evenly coating interior surfaces of cathodes.

Another object of my invention is to prevent heavy deposits of coatings.

Other objects and advantages of the invention will be apparent from the following description and drawing in which:

Fig. 1 is a view of one end of a sterilizing lamp with part of the casing broken away to disclose a type of electrode to which the invention is particularly applicable.

Fig. 2 and 3 are views, with the electrode in cross section, illustrating the preferred steps in applying the coating.

' One ofthe diificulties with coated cathodes or electrodes alternately acting as cathode and anode is to apply an even coat and especially to evenly coat an interior surface of a cold cathode. For purposes of illustration, I have disclosed in Fig. 1 such an electrode which is used in sterilizing lamps to act alternately as a cathode and anode. This electrode is more particularly described in Pat. No. 2,029,013, issued to P. W. Blackburn, January 28, 1936, for Cathode for discharge devices, and is especially adapted to illustrate the difliculties of satisfactorily coating similar electrodes or cathodes although my invention is not limited to the particular shape illustrated.

- The coating on the electrode is to make it a cathode and accordingly it will be referred to as such. The cathode illustrated comprises a cylindrical portion ID with a round open end I l and an interior cylindrical wall l2 illustrated in Fig. 2 which it is desired to coat with an electron emitting coating l3 illustrated in Fig. 3. The back part of the cathode, which is preferably of nickel, is

. pinched into a conical portion to provide integral fins l5 enclosing a conductive standard 16 secured'to a conductive end cap I! sealed to the tubular glass casing I8 of the lamp.

-The preferred coating for the interior of the cathode isa combination of two or more alkaline earths and preferably barium, strontium and calcium' put on in the form of carbonates in suspension with a binder such as nitrocellulose dissolved in diethyl carbonate and later reduced to the oxide as is well known. The most common ways of application are spraying, painting or dipping. In the spraying method, it is difilcult to apply a coating of definite weight, distribution and wetness because the method allows wide variation in both the mechanical and human elements.

The painting method permits very poor control of coating weight because the weight depends upon the degree to which the brush is saturated with the coating suspension and upon the skill of the operator.

The weight and distribution of the coating applied by dipping depends upon how much coating drips from the cathode, the position in which the cathode is placed after being clipped and upon the skill of the operator.

Any of these methods may leave a too thin a coating on one portion of the cathode wall and too thick a coating at other portions of the oathode wall. In regard to the particular type of cathode illustrated, coating material will generally be deposited on the inner conical wall l4. To heat treat the electrode and reduce the carbonate coating to an oxide, a high frequency coil surrounds the cylindrical portion 10 of'the electrode and heats it by induced currents. The integral fins l5 are efi'ective in dissipating heat during operation and this action will help maintain the conical portion l4 cooler especially if it is not surrounded by the high frequency coil. The carbonate deposit on the conical portion may accordingly not be reduced or completely reduced to the oxide. A heavy deposit of coating on the cylindrical walls also may not be completely reduced to the oxide.

These sterilizing lamps operate in a gaseous medium of mercury vapor and a gas such as argon, neon or helium to give a low starting voltage requirement. After the tube is sealed off and during long operation, the unreduced carbonates on the cathode wallmay give up carbon dioxide gas and this gas may seriously affect the starting characteristics of the tube. In fact the tube may not start on its original rated voltage.

Further, the evolved gas from partially or totally unreduced carbonates may react with mercury during operation and form a compound which plates the inner glass surface and reduces the ultra violet output of the lamp, reducing its efiectiveness.

According to my invention, I place the alkaline earth carbonate suspension on the inner cylindrical wall only of the cathode and revolve the cathode to distribute this coating evenly on the wall by centrifugal force. In order to distribute the desired weight or thickness of coating, I preferably utilize the apparatus illustrated in Fig. 2.

A syringe 20 is dipped into the carbonate sus- 3 pension and a considerable amount drawn into the barrel portion 2 I. The position of the plunger 22 on the scale gives the quantity in the syringe and also the difference in readings will give the amount extruded or drawn in the syringe. I prefer to construct the syringe with a long nozzle 24, longer than 1 the cylindrical portion of the electrode. The inside diameter of the nozzle portion as illustrated at the broken away portion is the size to contain the desired amount of suspension of alkaline earth compounds and binder per unit length as is desired per unit length for the inside surface. In other Words a length A of the nozzle contains the exact amount of suspension desired for a length A of the inner cylindrical surface of the electrode. Although a regular type of syringe may be used, I have devised the special type illustrated to make the application of the coating independentof the judgment of the operator. The-barrel portion. 2 is preferably long as indicated by the broken, lines 32. This barrel portion also has an inside diameter the same as the nozzle portion and as a continuation thereof. The plunger 22 is preferably a sturdy rod with a scale 34 marked thereon. The rear portion of the barrelterminates in an enlarged ring to which is secured the finger grip 36.

The barrel portion is placed in a groove 3'? of a support 27 with the front face of the enlarged ring against the rear face 21' -of the support. The support 2? has a rear extension 38 and on this extension 38 is an upright arm 39 adjustably clamped thereto as by-thenut id. This upright arm 39 has ashelf 6| upon Whichrests'the' extension of the plunger 22'. The upright arm has a rightangle extension 32 abovethe plungerl22 anda set screw 13 extending through this extension :32 to bind the plunger on the shelf ll of the upright arm 39.

The upright arm is adjusted on the extension 38'the' distance through which it is desired to move'the plunger which in this case, is -A' shown by the arrows on the right hand side equivalent to the A shown on the left hand side. The plunger 22 is then bound bythe set screw 43. The electrode is inserted" in the jaws 25 of a chuck and the nozzle 2 is then inserted in the electrode H) to the innermost position for depositing the material on the cylindrical surface but not on the conical portion H The distance for inserting the nozzle can be calculated and marked at on the nozzle. up this mark at 35 with trode.

The chuck and electrode isrevolved and'the-operator pulls back on the finger grip 35' until stopped bythe upright arm39. The nozzletip 3G by this movement hasheen pulled to the front edge I l of the electrode and has deposited exactly the suspension desired per unit length along the electrode. The centrifugal ierce-exerted by the revolving electrode .will'coatthesuspension evenly over the innercylindrical walls 'of'ithe The operator merelyli'nes. the'edge ll of the elec-- 4 The plunger 22 is released from the set screw 43 and the syringe moved up until the ring 35 rests against the rear face 21' of the support 21. The set screw 43 then binds the plunger 0n the shelf 41 and the apparatus is ready for the next electrode which has been inserted in the jaws of the chuck.

v The electrode which has been coated is positioned in the tube with the other elements and then the carbonate coating is reduced to an oxide by a high frequency induction coil placed about the tube where the electrode is located.

My invention deposits the right amount of coatiing in the right'places. The application of the coating by my invention is practically fool-proof because of very little demand on the intelligence of the operator in merely inserting the nozzle into the electrode up to a mark on the nozzle, and after pulling out the nozzle, resetting the set-screw 43 on another mark on the plunger 22.

While I have disclosed the preferred method and apparatus forcarryingout my invention, it is apparent that modifications may be made therein and accordingly, I desire only suchlimitations to be imposed thereon as is necessitated by the spirit and scope of the following claims.

I claim:

1. A coating process consisting of three simultaneous operations, namelypmoving a nozzle from which coating material is ejected in proximity to a surface being coated; forcingmaterialiromthe nozzle commensurate with movement of the nozzle; and spreading the material in-a direction; transverse to the movement of the nozzle. r

2. A coating process consisting oi-three simultaneous operations, namely;- -moving a nozzle from which coating material is ejected in proximity to a surface being coatedyforcing material from the nozzle commensurate with movement of the nozzle; and centrifugally spreading the material in a direction transverse to the movement of the nozzle.

3. A coating process for the interior of a tubular member consisting of three simultaneous opera-. tions, namely; moving a nozzle, from which coating material is ejected, longitudinally of and in one direction in proximity to the interior sur face of said tubular member-beingcoated; forcing coating material from the nozzle commensurate, with, and controlled in amount by, movement-of. the nozzle; and spinning the tubular member and thereby centrifugally spreadin the material zin. a direction transverse to the movement of the; nozzle. Y

4. A coating process for the interior of a tubular member, comprising three simultaneous opera-; tions, namely; moving a-nozzle from which coating material is ejected only as the nozzleis moved in one direction longitudinally of the tubular member, and in proximity totheinteriorisurfaoe of said tubular member being coated! forcing coating material from the-noz'zl'esby movement of the nozzle in the-said one direction-andi'ejectin'g an am'ount'wholly controlled by distanceof movement of the nozzle irrespective-of rate ofrmove ment of the said-nozzle with respect-.toithe' surfaceyand spinning the tubularmembenandthere by centrifugally spreading the material-in a direce tion. transversetothe-movement of. the nozzlelh.

i r 3 GEORGE-S. EVANS: i. a 

